The requirement for total joint replacement has increased significantly due in large part to the increasing age of the general population in which arthritic joints become more prevalent, and due to the increased physical activities of the general population. In response to this need, many advances in the field of total joint replacement, such as knees, hips, elbows, have been realized. Complication and failure rates have been markedly reduced, the quality of implant materials have been improved, and the indications for surgery have been refined. In spite of these advances however, total joint replacement has not been successful in the young, high demand or overweight patient.
The reason for this lack of success is because typically the prosthetic replacement is a selection of one size out of several available sizes. Secondly, where proposals have been made or attempted in the past involving a custom joint replacement, obvious shortcomings are apparent in the mismatch of the prosthetic replacement with the patient's joint geometry.
Presently, the usual procedure in total joint replacement is one in which the clinician selects the most suitable prosthesis for a given patient from a fairly large variety of commercially available prosthetic designs.
Most manufacturers of total joint replacements have based their designs on the replication of normal joint anatomy. However, the selection and attempt to match a particular patient with one of the commercially available prosthetic designs is most difficult since joint geometry is unique for each individual.
Information on the individual's joint geometry is available through standard non-invasive techniques, such as radiological, magnetic resonance and nuclear examination and imaging techniques. Generally, such techniques involve developing a medical image of the joint in two dimensional representations from which measurements may be taken and if desired three dimensional models can be constructed.
Proposals have been made for advanced systems in which displayed data from a computerized tomographic device (CT) is analyzed to define the bone from the surrounding soft tissue. Generally, such advanced techniques require a technician to interact with the displayed CT scan image to intelligently speculate with respect to the threshold of certain values represented by the displayed image so that the system can thereafter form the boundary between bone and surrounding soft tissue. Typically, the threshold value relates to either a single threshold value of radiological density determined in the CT scan process, or to a threshold range of such density values. These enhanced systems still provide errors of about 8% when compared against hand measured values of subject joints.
Thus, while the newer, enhanced systems represent an earnest attempt to provide a better design of custom joint replacements compared to the selection and matching process presently in use, because of the large errors, custom joint replacements are still not a viable design alternative to the present standard selection and matching techniques. Accordingly, in current practice, the choice of a prosthetic replacement is usually made on the basis of which prosthetic design the attending physician is most comfortable using based on his past experience.
Accordingly, it is desirable to provide a process for making custom joint replacements which are unique to an individual's joint geometry and therefore with significantly less errors than with prior techniques so that the customized joint components will achieve a greater degree of implant reliability and function.